This invention relates to an apparatus and a method of analysis for differentiating between different types of particulate matter.
During monitoring of air quality, and/or vehicle emissions, aerosol particulate matter may be collected on for example the piezo-electric crystal sensor of a mass sensitive microbalance by use of an electrostatic precipitator. A known microbalance is described in “Piezoelectrostatic Aerosol Mass Concentration Monitor,” by Olin J G, Sem G J & Christenson D L, Amer. Ind. Hyg. Assoc. J 32: 209 (1970). Particulate matter is collected on the sensor which records the weight of material collected. A problem with this type of analyzer is that it fails to distinguish between volatile and non-volatile particulate matter collected on the sensor. Volatile particulate matter may evaporate from the sensor over a longer or shorter time period, and different particles collected may be reactive, resulting in mass change on the sensor. Even real time microbalances have to be calibrated using non volatile particles.
For an air quality assessment, this problem is presently addressed by using an agreed factor determined by the EC Working Group on Particulate Matter to convert monitored readings into EU standard gravimetric readings. This factor has recently been set at 1.3, but trials have indicated that the factor varies between 1.0 and 1.6 depending upon the location of the monitor season.
Other particle analysis systems collect particles on a filter which is then weighed. This again cannot give any accurate indication of the mass of lost volatile particulates, or mass changes associated with chemical reactions occurring in the filtrate.
The present invention seeks to provide an improved analyzer and method of analysis for aerosols which gives a more accurate indication of the volatile particle content of the total particulate matter in the aerosol and the reactivity of the collected particles to both water absorption and chemical reaction.